As many as 83 million of Facebook’s 955 million accounts could be fake. And up to 1.5% of total accounts are likely “undesirable” profiles specifically set up for nefarious purposes, such as affecting ad results and spamming users.

Related

These revelations came from Facebook’s SEC filing, where the company laid out all of the potential threats to its future growth and profitability.

Facebook explains that the “undesirable” accounts “… represent user profiles that we determine are intended to be used for purposes that violate our terms of service, such as spamming.”

In the filing Facebook said that non-malicious duplicate accounts, which still violate the company’s user agreement, made up 4.8% of worldwide accounts. Additionally, accounts that are “user misclassified” — such as a Facebook profile for a pet — make up 2.4% of all accounts. Facebook’s user agreement states that if you want to set up a profile for a pet or other non-human object you must set up a “page” as opposed to a separate account.

According to the report, the problem of dubious accounts is a much bigger issue in emerging markets for Facebook, and less of a problem in more established areas.

“We believe the percentage of accounts that are duplicate or false is meaningfully lower in developed markets such as the United States or Australia and higher in developing markets such as Indonesia and Turkey,” Facebook said.

However, the company filing went on to clarify that “significant judgment” went into making this estimate, meaning it was kind of an educated guess.

Since Facebook’s primary revenue source is through advertising, determining the number of users on the service is key in knowing exactly how many eyeballs can be advertised to.

“The loss of advertisers, or reduction in spending by advertisers with Facebook, could seriously harm our business,” the company said in the filing.

The BBC reported publishing company Limited Press alleges that “80% of clicks on its advertisements within Facebook had come from fake users.”

In the weeks since Facebook’s initial public offering, the company’s stock has tumbled on fears the company could no longer maintain its meteoric growth and earn the high revenues required to justify the premium stock price.

Last week, Facebook reported results, but offered no outlook or forecast for the year, spooking investors who sought reassurance about growth in 2012.

Wall Street is also bracing for a potential deluge of millions of shares after August 16, when a post-IPO lockup period on employee share sales expires.

Despite having shed 40% of its value since a May 18 IPO, Facebook still trades at about 47 times forward earnings. Google, by comparison, trades at 15 times forward earnings.